In a gas distribution network, it is sometimes necessary to interrupt the flow of fluid when, due to some anomaly, the pressure in the network is on longer in compliance with the expected pressure and lies on the wrong side of a predetermined reference value. The reference value may correspond either to a maximum pressure or to a minimum pressure.
This safety and automatic stop function is performed by a member that is commonly called a "safety valve".
FIG. 4 shows a prior art embodiment of a safety valve installed on a pressure regulator.
The function of a pressure regulator is to adjust the pressure of the fluid passing through it. This adjustment is performed either as a function of the pressure of said fluid as measured downstream from the regulator, in which case it is called a "pressure-reducing valve", or as measured upstream from the regulator, in which case it is called a "release valve", or else as a function of a pressure measured in another fluid. When greater accuracy is desired in the adjustment, a second member called a "pilot valve" is associated with said first regulator, and is constituted by a pressure-reducing valve that deals specifically with the pressure control signal for the actuator of the regulator. The assembly is then called a "pressure-reducing regulator".
As shown in FIG. 4, a regulator assembly fitted with a safety valve mainly comprises three portions: a central portion 1 which constituted both the body of the regulator and the body of the safety valve; a top portion 2 which constitutes the actuator of the regulator; and a bottom portion 3 which comprises the control means for the safety valve per se.
The assembly also includes pressure-reducing valves 4 and 5, throttling cocks 6 and 7, and a pressure-measuring device 3 enabling the pressure to be adjusted in a main duct 9 having the safety valve installed therein by means of upstream and downstream connection flange 10 and 11 respectively on the body 1. In conventional manner, the body includes a central orifice 15 disposed perpendicularly to the flow of the gas flowing along the duct 9, with the top end 16 of the orifice constituting the set of the regulator valve and with the bottom end 17 of the orifice constituting the seat of the safety valve.
The actuator 2 of the regulator valve is provided with a diaphragm 20 which is displaced under the effect of opposing forces exerted by a spring 21 counteracting the pressure taken downstream from the regulator and safety valve assembly, thereby vertically displacing the valve member 22 of the regulator valve by means of a push rod 23.
The portion 3 for controlling the safety valve essentially comprises a mechanism housing 30 and a pressure-measuring housing 31. The mechanism housing includes a detection stage 32 and a power stage 34 which acts on a control rod 35 having the valve member 36 of the safety valve fixed to the end thereof. This two-stage mechanism guarantees the accuracy with which the shutter 36 is tripped under the control of the pressure-measuring housing 31 responding to a pressure threshold determined by the setting of a spring 37. An incorporated lever 38 enables the trip mechanism to be reset after it has tripped.
In another example of the prior art (not shown), the mechanism may be tripped manually by a pushbutton, for example, and the pressure of the circuit to be controlled may also be adjusted by means of maximum and minimum pressure springs set to prefixed values.
Although those devices perform the function for which they are designed properly, they nevertheless suffer from numerous drawbacks.
Firstly, the device for locking the safety valve is often complex and fragile because of the numerous levers included in its mechanism housing for the purpose of multiplying the force generated by the valve spring, thereby limiting reliability in particular, and consequently reducing the level of safety that can be expected from such a device. In addition, this fragility of the mechanism requires its various levers to be adjusted minutely, and any clumsy handling quickly leads to breakage, which happens frequently when the device is put back into operation manually, in particular because of the forces exerted by the manual resetting lever. Likewise, the condensation associated with the expansion of the gas gives rise to a high degree of oxidation of these various mechanisms, and sometimes also causes them to be jammed by the formation of ice. Finally, these various operations require an operator to act directly on the device which makes it impossible for such a device to be used in buried expansion stations, for example.
An object of the present invention is to remedy the above-mentioned drawbacks and to provide a safety and automatic stop device which is also usable in buried expansion stations and whose overall reliability is greater than that of previously-existing devices.